Typical of the relevant prior art is German Patent 3,923,574, which discloses a pallet switching mechanism in which a pallet changer comprises a power-driven support structure adapted to be lifted and lowered and including a pallet driver rotatably mounted thereon for changing a pallet disposed on a machine table for a pallet held at the stand-by position. Fixing of the pallet on the machine table is effected by way of several locking and setting bolts arranged on the pallet which are fixedly held in the machine table by a hydraulically operated clamping unit. This mechanism has the drawback that a separate hydraulic drive mechanism is required for operating the pallet fixing means. The pallet changer drive means and the hydraulic drive means for the fixing device are separately actuated and must be matched with each other in a suitable way. A complex control system is therefore required for operating and matching the two separate drive means.